There's often a significant lag time between the ceremony and reception thanks to the inevitable post-wedding pictures or scheduling requirements by the venue (the church ceremony was at 2:30 p.m., but the reception site doesn't open until 5:00).
In cases like this, some people opt to skip out on the reception altogether and head home to comfy clothes and slippers. Avoid this issue by keeping guests actively engaged in the ceremony or reception site during the downtime. Getting married at a big park? Arrange for 10-minute horse and carriage rides or rickshaw tours. After ceremonies at a museum or botanical garden, have an expert offer brief tours of different wings or one of the various gardens. In fact, I just returned from a reception held at literally one of the wildest party places in the world: the San Diego Zoo. Each guest had a complimentary ticket to visit the zoo during the two-hour gap between the ceremony and reception. Sure, we looked strange trolling around in cocktail dresses and ties, but we probably impressed the giant pandas with our impeccable fashion sense.